S3: view bucket contents without ListBuckets permission

from aws/aws-toolkit-jetbrains/issues/2610

## Problem

> My profile has access only to certain bucket in my organization, so with that limited access I am unable to use the AWS Explorer for S3.
> It would be great to allow manually adding the limited resources I have access to so I can explore them in the UI. Otherwise I'm back to CLI

## Proposal

Add a `View Bucket` action to the S3 node itself allowing inserting of a bucket or S3 URI

Start at the S3 node in AWS Explorer and trace how bucket contents are currently discovered. Review the proposed View Bucket flow for a bucket name or S3 URI, then verify it with credentials lacking ListBuckets permission. Done means an authorized limited-access user can open the specified bucket without requiring ListBuckets.

Written by the indexing model from the issue text.